Understanding Eye Tracking & How it Can Work for You: Definitions, Metrics, and Applications

Eye tracking is a key technology to help us understand human behavior and the underlying thinking processes. Its applications are limitless, both in research and commercial use.

Overall, eye and gaze tracking technology provide invaluable insight and opportunities. To unpack its complexity, let’s explore the fundamental questions of what is eye tracking, how it works and what are its applications.

What is Eye Tracking?

Eye tracking is a technological process that enables the measurement of eye movements, eye positions, and points of gaze. In other words, eye tracking identifies and monitors a person’s visual attention in terms of location, objects, and duration.

Eye tracking technology is often mentioned in relation to:

  • Measurement of blinking patterns
  • Identification of what a subject ignores/does not look at
  • Assessment of pupil reaction when presented with visual/emotional stimuli
  • Facilitation of human-computer interaction and machine learning.

Eye Tracking and Gaze Tracking Basics

The premise on which eye tracking technology was founded on is:

Humans communicate via eye contact. By passing that very attribute on to computers, they will be able to function in a more human-like manner. Click To Tweet

To do so, psychologists studied, in detail, the physiology and anatomy of the eye and the cognitive operations associated with the visual system.

Anatomical Aspects

The brain processes images through light-sensing cells in the retina. These rod cells and cone cells detect light that comes in through the pupil and send the visual data to the brain.

While there are far fewer cone cells than rod cells in the retina, the former permit humans to see in high resolution and full color.

eye anatomy

Source: Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014“. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

Cone cells are in the fovea, the center of the visual field. The fovea is the region with the highest visual acuity in the eye, but it is notably small. Outside the area of foveal vision is the peripheral region, where clarity decreases significantly.

As a result, to process detailed visual information of interest, the eye has to move.

The compromise of having a high-resolution central vision and low-resolution peripheral vision is what enables eye tracking technology, to begin with.

Eye Movements

The eye executes a number of movements, such as vergence or torsional. However, the most pertinent ones measured through eye tracking are fixations, saccades, and smooth pursuit.

Fixations occur when the eye stops to collect visual data. Although the duration of one is highly variable, the longer a fixation is, the more visual information is processed.

Saccades are fast “jumps” that the eye performs between fixations in a static environment. The eye moves from one object of interest to another with the goal of acquiring new visual data in high resolution.

Due to the extreme speed of saccades, vision is suppressed. Thus, they are not as significant in gaze tracking as fixations are. Yet, they do reveal information about the course of fixations and visual attention.

Smooth pursuit is the eye movement that takes place when looking at an object in motion and following it. As visual intake is possible during smooth pursuit, the movement is relevant for eye tracking.

Pupil Size

Additionally, video-based gaze tracking allows the measurement and analysis of pupil size. To get accurate pupil tracking data, the environment needs to be rigorously controlled.

Inadequate test conditions, pupil dilation can be observed and monitored as a result of:

  • Strong emotional stimuli
  • Acute attention
  • Illumination
  • Working memory load

Visual Attention

Most importantly, eye tracking facilitates the study of visual attention.

Due to the limited nature of image processing resources, the brain selectively chooses relevant visual information based on:

  • Interest – the conscious or unconscious decision to look at an object
  • Environment – elements detected through peripheral vision

In academia, the examination of visual attention leads to understanding of attention mechanisms in general. It sheds light on the cognitive processing that takes place during the execution of a given task.

For the same reason, eye tracking and attention analysis are valuable within the realm of commercial operations too.

Is eye tracking used for qualitative or quantitative research?

In the context of research methods, eye tracking is used for both qualitative and quantitative research.

Qualitative research

Quantitative research

Behavior interpretation Dependent variable
Usability (UX/UI) A/B testing
Retrospective interviews Stimuli measurement 

Standard vs. 3D Eye Tracking

While standard eye tracking faces a series of limitations, 3D eye tracking for depth sensors solves the challenges with the following solutions:

  • Wide range
  • Multi-person tracking
  • 3D line of sight
  • No calibration
  • Software only (if device integrates 3D camera)

At the time of writing this piece, Eyeware is the only company in the world that publicly offers a commercial eye tracking solution for 3D cameras.

Eyeware’s real-time 3D gaze coding software GazeSense offers an easy solution for getting quantitative and qualitative eye tracking data. Discover here how it can help your business, industrial, or research endeavors – gazesense.com.

How Does Eye Tracking Work?

Eye tracking works by following the eye position and movements non-intrusively. A source of invisible near-infrared or infrared light illuminates the pupil. Thus, a reflection generates on the cornea. An infrared camera will then record that reflection, delimit the center of the pupil, deduce eye rotation, and determine gaze direction.

Pupil Center Corneal Reflection (PCCR) is the formal term for the main method eye tracking uses, in which the pupil and corneal reflections are optically monitored.

The eye position, point of gaze, and eye movements are all calculated using advanced mathematical algorithms.

After that, the recorded information becomes raw data that eye tracking software subsequently processes.

Calibration

To achieve precision and accuracy in eye tracking, the user needs to take the lack of alignment between the optical and visual axes into consideration. While the optical axis is visibly measurable, the fovea’s location is off by a few degrees.

visual and optic axes

Source: Dorland’s Medical Dictionary for Health Consumers. (2007).

This requires correction (calibration) to ensure that the positions of the pupil and gaze align.

Before starting an experiment, the system calibrates by monitoring the pupil positions for one or more predefined points.

Data

Following the calculation of a gaze point, the raw data appears in the form of an XY coordinate. The XY coordinate indicates where a participant is looking on the screen. Then, the gaze tracking outputs coordinates according to its frame rate speed.

Software tools are typically used for eye tracking and processing data, namely identifying fixations and saccades. Fixations often show up as dots with sizes corresponding to the duration of the movement. Saccades are the lines that connect the fixation-dots. 

These actions can help clean the raw data before generating visualizations:

  • Reduce noise density
  • Improve precision
  • Apply an eye movement classification algorithm

Metrics & Visualizations for Eye Tracking Data Analysis

From static to animated representations, eye tracking and gaze tracking use a variety of metrics and visualizations for inspecting the data collected.

Fixations

Together with saccades, fixations create a scanpath, i.e., the path that a subject’s eyes follow. Additionally, eye tracking permits the measurement of:

  • Time to first fixation (TTFF) – the time between the onset of a stimulus and the fixation within an area of interest (AOI). This provides insight into visual attention.
  • First fixation duration – total time of first fixation
  • Fixation count – how many fixations took place inside an AOI
  • Average fixation duration – the higher the average fixation duration, the more attractive an AOI is for the respondent
  • Fixation sequences – comprised of fixation location and time of fixation

Gaze points & plots

While a gaze point reveals where a respondent is looking, a gaze plot facilitates the visualization of the scanpath. Gaze path plots depict the chronological order in which fixations and saccades were performed.

Aggregated gaze plots are used to assess the scanpaths of multiple respondents to ultimately identify behavior patterns.

Areas of Interest (AOI)

To assess different fixation metrics, areas of interest (AOIs) are used to select specific regions in a scene.

dim eye tracking area of interest
Dim light – in-car environment
bright eye tracking area of interest
Strong light – office environment

For delimitation, the AOIs are drawn on the image, around the elements chosen for comparison.

  • Ratio – the number of participants who fixated on an AOI
  • Dwell time – how much time was spent viewing an AOI, i.e., duration of observation
  • Observation count – the number of times a participant revisited an AOI

Heat maps

As a visualization tool, a heat map illustrates how fixations and gaze points are distributed. Green, yellow, and red tones are used to show the density of gaze points in specific parts of the AOI.

eye tracking heat map light
White background heat map sample
eye tracking heat map dark background
Black background heat map sample

Eye tracking and heat maps work on the principle that the more fixations take place in a certain area, the redder the region will be.

Focus/opacity maps

An opacity map, also known as a focus map, shows the same information as a heat map but in a different manner.

Instead of covering the areas that received the most visual attention, a focus/opacity map highlights them clearly. In turn, the areas with the fewest fixations are darkened.

Measures

The standard unit of measure in eye tracking is gaze points:

1 gaze point = 1 raw eye tracking sample

E.g.: 60 Hz sampling rate = 60 separate gaze points/second (1 gaze point/16.7 milliseconds)

A consumer eye tracking device has a sampling rate that can vary from 30 to 60 Hz. Research-dedicated units can track at about 120 Hz to 1000 Hz (and some even up to around 2000 Hz).

Eye movement speed and frequency averages are:

  • Fixation
    • From 100 to over 600 milliseconds
    • Usual duration: 100-300 milliseconds
    • Typical frequency: around 3 Hz
  • Saccade
    • From 20 to 120 milliseconds
    • Usual duration: 20-40 milliseconds
    • Up to 600-700 degrees/second
    • Typical frequency: 4 times/second at about 4 Hz rate
  • Smooth pursuit – up to 30 degrees/second

Hardware & Software: Gaze Tracking Tools

Eye tracking and gaze tracking need a device to capture information and a system to track and process it, i.e., hardware and software.

What is Eye Tracking Software?

Although the features vary from one brand to another, there are typically two types of software that need to be used in the standard eye tracking process:

  • Software for acquiring and recording data
  • Software for processing and analyzing data

Furthermore, depending on the developer, dedicated software might be needed for:

  • Different types of eye trackers (e.g. glasses vs. screen-based)
  • A specific eye tracker
  • Different stimuli (e.g. static vs. dynamic)

However, there are several integrated software solutions available for both data acquisition and analysis.

Regardless of the software chosen, some key features to consider are:

  • Accuracy
  • Calibration time
  • Optimal distance
  • Latency
  • Sampling rate
  • Tracking angles
  • Head movement range
  • Recovery time

Eye Tracking Without Glasses: How Does Eyeware’s 3D Gaze Tracking Work?

The state-of-the-art eye tracking software solution provided by Eyeware uses depth-sensing cameras to ease human-machine interaction in 3D.

GazeSense annotates 3D objects of interest and outputs data in real-time for simultaneous multi-person studies. As a result, it delivers information about attention, intention, interest, and engagement.

Without requiring glasses or other wearable trackers, the award-winning software works with a variety of consumer and custom devices with depth sensor technology. From smartphones to development kits, laptops or gaming peripherals, GazeSense is compatible with stereoscopic, structured light, and ToF cameras, as well as custom 3D sensors.

The 3D gaze tracking software has applications in many fields, such as automotive, robotics, consumer devices, gaming, retail, and advertising.

To find out how GazeSense can optimize your commercial or academic efforts through multimodal human-machine interaction, contact our Customer Success Specialist.

Hardware: What is an Eye Tracker?

Fundamentally, standard 2D eye tracking requires a device to measure activity, known as an eye tracker.

Today, eye trackers are either remote (screen-based) or mobile/wearable (head-mounted devices, such as glasses or virtual reality headsets).

Remote: Screen-based devices

When tracking eye activity at a distance in a controlled environment, screen-based devices are typically used.

The participant sits in front of a computer monitor or laptop, which has a panel or stand-alone unit mounted below or otherwise near the screen. Then, the participant is presented with multimedia stimuli – like photographs, websites, videos or games – to trigger, record, and analyze eye movements.

Overall, screen-based eye trackers provide visual attention insights for developers or researchers by collecting high-quality eye-related information in a static test setting.

Mobile: Eye tracking glasses & VR headsets

Wearable eye tracking devices are recommended for behavioral studies in real-world scenarios. They permit movement beyond the “headbox” limitations imposed by stationary eye trackers.

Head-mounted eye trackers can measure eye movements from up close. Nonetheless, mobile trackers like eyeglasses can become unstable in certain test conditions, such as participants playing sports.

In VR applications, eye tracking can allow the respondent to control features by merely looking at a particular virtual button

VR headsets with gaze tracking can be used for:

  • Professional training in industrial fields
  • Interactive entertainment
  • Testing visual attention in retail, and more.

eye tracking virtual reality experience

All in all, if experiments need participants to respond in natural, dynamic surroundings, wearable eye tracker devices are the best solution.

Eye Tracking vs. Head Tracking

The difference between eye tracking and head tracking is simple.

While both processes involve monitoring positions and movements, the former only tracks the eyes while the latter records only head activity.

When combined, the two technologies provide even more valuable data and create a rich user experience in applications like gaming.

Research & Applications: How Does Eye Tracking Work in Real-world Situations?

Technically speaking, almost any scenario with visual elements can benefit from eye tracking and gaze tracking. Click To Tweet

So far, the technology has been used to make tremendous advancements in cognitive science, neuromarketing, AI, workplace safety, and many other research and business fields of interest.

Eye Tracking Fields of Use: What is it used for?

As predicted, eye tracking has already revolutionized the way humans communicate with devices and vice-versa.

Yet, we still need to develop eye tracking technology so every standard consumer device will be equipped with it. Until then, it continues to assist academics, developers, and advertisers in gaining unparalleled insight into conscious and subconscious human behavior.

Research

As already mentioned, eye tracking has significant contributions to both qualitative and quantitative research. In an academic context, the technology can be used as a tool for:

  • Visual behavior study
  • Attentional mechanisms evaluation
  • Visual stimuli response measurement
  • Learning patterns insight
  • Group behavior comparison

Automotive

Eye tracking plays a major role in safety in the automotive industry. The technology can help detect if the driver is drowsy or distracted, and help prevent car accidents.

With 3D eye tracking, the driver is monitored and assisted through gaze-supported interaction. Click To Tweet

By incorporating the technology into smart dashboards, features like augmented reality HUDs and virtual co-pilot become a central part of the driving experience.

Psychology

Within the field of psychology, gaze tracking enables the study of cognitive processes. Examples include memory, problem-solving, language, decision-making, perception, and attention in general.

Neuroscience uses eye tracking for the study and early detection of diseases like Parkinson’s, schizophrenia, Alzheimer’s, or autism. For example, technology has helped researchers demonstrate the recognition and comprehension of complex emotions in adults with ASD.

Neuromarketing & Advertising

As eye tracking technology facilitates the study of visual attention, it has become a useful tool for neuro marketers and advertisers on a broader scale.

In both online and offline applications, gaze tracking helps determine what customers are naturally most interested in and what they might ignore altogether.

Furthermore, neuro marketers now use eye tracking and facial coding to measure emotions when exposed to multimedia stimuli.

Video Games & Entertainment

Foveated rendering, enveloping graphics, and extended gaze control are all cutting-edge features in the gaming industry that are possible through eye tracking.

The user can explore the environment through their gaze and interact with various elements of the game just by looking at them.

Similarly, for several years now, individuals have been able to control televisions based on the same principles.

Accessibility

Through eye tracking, people with disabilities can control computers and mobile devices and even create digital art. Individuals who cannot move or speak can communicate with machines through eye movements.

The technology has greatly improved accessibility and empowered disabled users to perform a variety of computer-related tasks.

Retail

Professionals in retail can also use eye tracking to generate shelf attention analytics. In other words, gaze tracking technology provides insights into shopper behavior and the buying decision process. Click To Tweet

As a result, retailers can make notable improvements in terms of display, store, and packaging design, as well as layout and distribution.

What Are the Pros and Cons of Eye Tracking?

Without a doubt, the advantages of eye tracking technology are bountiful.

Benefits

  • Advancements in fields like AI, social sciences, and healthcare
  • Assistive technology for individuals with limited mobility
  • User interface and experience improvements
  • Ensuring safety in hazardous work environments
  • High-quality market research findings
  • Remarkable insights into the human mind and body, when used with more biosensors like:
    • FEA (Facial Expression Analysis)
    • ECG (Electrocardiogram)
    • EEG (Electroencephalogram)
    • EDA (Electrodermal Activity)
    • EMG (Electromyograph)

As eye tracking continues to be a developing technology, there remains a multitude of challenges that need to be approached.

Difficulties

  • The Hawthorne Effect – a person changes their behavior knowing they are under observation (e.g., a research study in a test environment)
  • Interpretation (e.g., a higher or lower number of fixations can state different conclusions based on context)
  • Squinting – the Pupil Center Corneal Reflection (PCCR) method is not effective when a participant squints
  • Midas touch problem in gaze-controlled interfaces – when a user unintentionally triggers an undesired action
  • Easier calibration for standard eye tracking

Best Practices & Ethics

Conducting eye tracking studies and experiments have a learning curve. 

Just a few of the procedures and ethical considerations that should be acknowledged beforehand are:

  • Inform each participant about the purpose, procedures, potential risks (if any) and benefits of an experiment
  • Ensure that every participant provides his or her full consent to take part in the study
  • Prepare an effective test environment – balanced light, removal of distractions, adjusting equipment
  • Train the participants to be familiar with the equipment and procedures

Is Eye Tracking Worth Exploring?

Absolutely.

Since its initial development, eye tracking technology has paved the way for monumental progress in countless fields.

The gaze tracking industry projects continuous growth over the next years helping: 

  • R&D engineers find real-world solutions with cutting-edge technology
  • Innovation leaders implement creative, state-of-the-art solutions
  • Developers build more effective systems to solve current and imminent challenges  
  • Marketers create POCs and enhance the consumer experience
  • Professors and researchers break new ground and pave the way for a better world
  • Neuroscientists gain unprecedented insight into serious cognitive disorders
  • Students contribute to developing the technology of the future

We would be glad to help you try real-time 3D gaze coding with our software. Reach out to the Eyeware Team with a direct message.